Added metrics averaged over intervals of the loss/bandwidth reports, to be used for adjustment of robustness settings. Separated this set
from the (global) metrics used for resolution adaptation.
Some code cleanup in content_metrics.cc/.h.
Review URL: http://webrtc-codereview.appspot.com/52002
git-svn-id: http://webrtc.googlecode.com/svn/trunk@125 4adac7df-926f-26a2-2b94-8c16560cd09d